Gedmatch and G25 in many cases is a farce

[Peterski]

They surely use IBD for assigning regions (which they started doing around the Spring or Summer of 2018).

But this method is not perfect either because it cannot tell the exact cause-effect relationship of a DNA match.

For example, I scored "Tyumen Oblast" among my regions and I'm 99% sure that I don't have any ancestors from there, on the other hand I'm also sure that some Poles who were sent to Siberia in the 19th century (as punishment for uprisings against Russia) ended up there.

So my match to Tyumen Oblast is most likely because of some Polish DNA there. Or, something ancient.

In general all Europeans share a lot of IBD with each other.

Obviously they show only IBD shared with nations counted as "East Euro" category under this category.

For my French-German, they show two regions in Germany as well as "Grand Est" and "Hauts de France".

These French regions might also be due to Polish migrants there (at least this is what mlukas suggested).

[Lemgrant]

The reason why some North Africans score 0% SSA on 23andMe is segment smoothing.

Let's say we have five segments, each one with 200 markers (SNPs):

1. - 156 North African markers, 44 SSA markers = all segment, 100% of the segment (all 200 markers) assigned to North Africa
2. - 101 North African markers, 99 SSA markers = all segment assigned to North Africa
3. - 190 North African markers, 10 SSA markers = all segment assigned to North Africa
4. - 135 North African markers, 65 SSA markers = all segment assigned to North Africa
5. - 183 North African markers, 17 SSA markers = all segment assigned to North Africa

^^^
After segment smoothing, all five segments (all 1000 markers) will be assigned fully to North Africa.

The final result is, that this person scores 100% North African and 0% SSA (on these five segments).

If there are segments in which he has for example 120 SSA markers and 80 North African, then these segments are assigned Sub-Saharan, of course.

=====

And now why AncestryDNA is different? Because they do not use this segment smoothing method.

And probably they don't run admixture on each segment separately, but on all of the DNA at once.

Edit:

Segment smoothing is also why Mortimer was scoring just 2% South Asian on 23andMe at one point. His South Asian markers are very dilluted in his DNA.

But after recent updates, it seems they have increased his South Asian to >10% again (which is surely more accurate for him, than that ridiculous 2%).

now this looks good, but this is the result on 50% confidence level. Also North Africans scored a lot European Iberian before the latest update on 23andme ~over 20% (user Adamm for example), but now 0%.

[marco]

The reason why some North Africans score 0% SSA on 23andMe is segment smoothing.

Let's say we have five segments (numbered 1. to 5.), each one with 200 markers (SNPs):

1. - 156 North African markers, 44 SSA markers = all segment, 100% of the segment (all 200 markers) assigned to North Africa
2. - 101 North African markers, 99 SSA markers = all segment assigned to North Africa
3. - 190 North African markers, 10 SSA markers = all segment assigned to North Africa
4. - 135 North African markers, 65 SSA markers = all segment assigned to North Africa
5. - 183 North African markers, 17 SSA markers = all segment assigned to North Africa

^^^
After segment smoothing, all five segments (all 1000 markers) will be assigned fully to North Africa.

The final result is, that this person scores 100% North African and 0% SSA (on these five segments).

If there are segments in which he has for example 120 SSA markers and 80 North African, then these segments are assigned Sub-Saharan, of course.

=====

And now why AncestryDNA is different? Because they do not use this segment smoothing method.

And probably they don't run admixture on each segment separately, but on all of the DNA at once.

Edit:

Segment smoothing is also why Mortimer was scoring just 2% South Asian on 23andMe at one point. His South Asian markers are very diluted in his DNA.

But after recent updates, it seems they have increased his South Asian to >10% again (which is surely more accurate for him, than that ridiculous 2%).

Ssa is clear in Some North Africans but didn’t see them score it in 23 and me very good break down and very disappointed to see this from 23 and me

[Peterski]

now this looks good

This is nothing new, Sikeliot started a thread about it here long ago and user Kurd (= Zoro?) on Anthrogenica:

https://www.theapricity.com/forum/sh...ity-components

Also North Africans scored a lot European Iberian before the latest update on 23andme ~20% (user Adamm for example), but now 0%.

Adamm's European fell from 20% to 0% in the same update in which Mortimer's South Asian fell from 15% to 3%.

But it seems they later updated Mortimer's South Asian again upwards. Did Adamm's European stay at 0% ???

[Lemgrant]

This is nothing new, Sikeliot started a thread about it here long ago and user Kurd (= Zoro?) on Anthrogenica:

https://www.theapricity.com/forum/sh...ity-components



Adamm's European fell from 20% to 0% in the same update in which Mortimer's South Asian fell from 15% to 3%.

But it seems they later updated Mortimer's South Asian again upwards. Did Adamm's European stay at 0% ???

no, it was 20% and fell to 0% in the latest update, while for Mortimer the south Asian score increased.

[Peterski]

no, it was 20% and fell to 0% in the latest update, while for Mortimer the south Asian score increased.

For Mortimer it first declined from 15% to 3% and then in another update it increased back from 3% to ca. 10%.

For Adamm it declined from 20% to 0% in the same update as for Mortimer, and later it probably stayed at 0%.

[Lemgrant]

For Mortimer it first declined from 15% to 3% and then in another update it increased back from 3% to ca. 10%.

For Adamm it declined from 20% to 0% in the same update as for Mortimer, and later it probably stayed at 0%.

his new results: https://www.theapricity.com/forum/sh...-phase-testing

his previous results: https://www.theapricity.com/forum/sh...rber-Moroccan)